KR100963366B1 - Titanium electrode material - Google Patents

Abstract

On the surface of the titanium alloy base material containing a noble metal element selected from the platinum group element, Au, and Ag, a mixed layer of the noble metal element and titanium oxide precipitated from this titanium alloy base material having an average thickness of 200 nm or less is formed, and this mixed layer surface and titanium The titanium material for electrodes characterized by the alloy base material having electroconductivity set to 12 m (ohm) * cm <^2> or less by the contact resistance value by the following measuring method.

Contact resistance is a mixed layer is formed plate-like titanium dioxide-sided material alloy, the other across a carbon cloth having an average thickness of 0.3mm, the contact area of the titanium alloy and the titanium alloy material from the upper side from 1cm ² of the copper electrode and the titanium alloy material lower when a sending a contact area with the alloy material 1cm put into ^two copper electrodes, and then, the titanium alloy material at a surface pressure load of 5kg / cm ² from the upper and lower sides state, flowing a current of 7.4mA between the two copper electrodes, The voltage drop between both carbon cloths is measured and calculated using a four-terminal ohmmeter.

Description

Titanium material for electrode {TITANIUM ELECTRODE MATERIAL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium material for electrodes, and more particularly, to a method of manufacturing a titanium material for electrodes suitable for separators for fuel cells. The titanium material for electrodes of this invention mainly aims at a plate or wire of titanium.

A solid polymer fuel cell is constructed by stacking a plurality of single cells through an electrode called a separator (or bipolar plate), with a single polymer sandwiching a solid polymer electrolyte membrane between an anode electrode and a cathode electrode.

The separator material for this fuel cell is required to have a property that the contact resistance is low and that it is held for a long time during use as the separator. From this point of view, application of metal materials such as aluminum alloys, stainless steels, nickel alloys, titanium alloys, and the like has been studied.

However, when these materials are used as fuel cell separators, the conductivity tends to be significantly degraded by an oxide film or the like formed on the surface thereof. For this reason, even if the contact resistance at the beginning of use is low, it cannot hold | maintain it for a long time during use as a separator, and there exists a problem that a contact resistance rises over time and causes a current loss. There is also a problem such as deterioration of the electrolyte membrane by metal ions eluted from the material due to corrosion.

With respect to such a problem, a technique has been conventionally proposed to maintain the conductivity by suppressing the increase in contact resistance. For example, it is proposed to form a conductive ceramic film on a metal surface, to suppress metal corrosion and to form a conductive ceramic film on a metal surface that maintains conductivity (see Patent Document 1).

After removing the passivation film from the metal surface, the surface is coated with a noble metal by plating or the like to maintain conductivity, compressing after the noble metal coating, and performing anticorrosive treatment in an active gas atmosphere (see Patent Document 2).

Patent Document 1: Japanese Patent Application Laid-Open No. 1999-162479

Patent Document 2: Japanese Patent Application Laid-Open No. 2003-105523

Disclosure of Invention

Problems to be Solved by the Invention

According to these prior arts, the durability as a separator can be secured to some extent, but is still insufficient in terms of characteristics such as conductivity retention (low contact resistance is maintained for a long time during use as the separator).

For example, in the case of Patent Literature 1, since the ceramics are fragile, cracks are likely to occur in the ceramic film due to any impact or the like. If a crack occurs in the ceramic film, a corrosive substance penetrates therefrom, and the substrate (metal) is corroded, which causes peeling or cracking of the ceramic film, and furthermore, a contact resistance rises, thereby degrading conductivity.

In the case of patent document 2, there exists a problem that a noble metal thin film layer peels locally and electroconductivity falls. That is, since the separator is usually made of irregularities, it is difficult to uniformly compress the noble metal thin film layer during compression processing after the noble metal thin film layer is formed. For this reason, during compression molding after the formation of the noble metal film, cracks occur in the noble metal layer or local residual stress occurs in the noble metal film, which causes this to locally peel off the noble metal thin film layer, further increasing the contact resistance. There is a problem that the conductivity is lowered.

This invention is made | formed in view of such a situation, The objective is to provide the titanium material for electrodes which is low in contact resistance value and whose electroconductivity is stable over a long period of time.

Means to solve the problem

Summary of the Invention The titanium material for electrodes according to the present invention for achieving the above object is a titanium alloy having an average thickness of 200 nm or less on the surface of a titanium alloy base material containing one or two or more precious metal elements selected from platinum group-based elements, Au and Ag. The mixed layer of the noble metal element and titanium oxide which precipitated from the base material is formed, and this mixed layer surface and a titanium alloy base material have electroconductivity which becomes 12 m (ohm) * cm <^2> or less with the contact resistance value by the following measuring method.

Here, the contact resistance is that both sides of the plate-shaped titanium alloy material on which the mixed layer is formed, each having a carbon cloth cloth having an average thickness of 0.3 mm therebetween, and the contact area with the titanium alloy material from the upper side of the titanium alloy material is 1 cm ² . The copper electrode and the titanium alloy material were inserted into the copper electrode having a contact area with the titanium alloy material of 1 cm ² from the lower side, and then, by a hydraulic press, the copper electrode and the carbon cloth were sandwiched between the upper and lower sides of the titanium alloy material. The voltage drop between the two carbon cloths when a current of 7.4 mA was flowed between the two copper electrodes while a surface pressure of 5 kg / cm ² was loaded was measured and calculated using a four-terminal ohmmeter. Shall be.

In addition, the said platinum group type element is 1 type, or 2 or more types of elements chosen from Pd, Pt, Ir, Ru, Rh, Os.

Effects of the Invention

In this invention, the surface layer (film) provided in the surface of the titanium material for electrodes is made into the mixed layer of the noble metal element derived from a titanium alloy base material, and titanium oxide. More specifically, a mixed layer of a titanium oxide substrate which is previously contained in the titanium alloy substrate and is newly produced by heat-treating the precious metal element (crystal or particle) precipitated from the titanium alloy substrate and the titanium alloy substrate which precipitated the precious metal element. It is done.

In this respect, the surface layer of the titanium material for electrodes of the present invention is completely different from the above-described prior art, and a film made of a material different from the titanium material such as a conductive ceramic film or a precious metal plating coating on the surface of the titanium material (titanium alloy substrate) Or sheaths are not installed separately from the outside.

Thereby, the problem of the adhesiveness and peeling of the film | membrane and coating which inevitably have in the point which said prior art coat | covers a heterogeneous material separately is eliminated. In the conventional case of separately coating a dissimilar material, when using the used material as a scrap (dissolution raw material of a titanium alloy) as an electrode, the dissimilar material is separated from the titanium alloy of the base material and then reused as a dissolution material of the titanium alloy. There is a need. In this respect, the recyclability is inferior to that of the present invention which does not cover different materials.

Furthermore, as in the present invention, the mixed layer of the noble metal elements (crystals and particles) and the titanium oxide derived from the titanium alloy base material has excellent conductivity of ¹² mΩ · cm ² or less in the contact resistance value by the measuring method as described later. In addition, since corrosion resistance and durability are good, this electroconductivity (conductive characteristic) is stable over a long period of time.

As in the present invention, the surface of the mixed layer and the titanium alloy substrate are the same unless the surface layer (film) provided on the surface of the titanium material for electrodes is a mixed layer of noble metal elements (crystals and particles) derived from the titanium alloy substrate and the titanium oxide. It cannot have the outstanding electroconductivity and stability over the long term which are 12 m (ohm) * cm <^2> or less in contact resistance value by a measuring method.

The contact resistance value by the said measuring method selects strict conditions also as a measuring method and a contact resistance value. For this reason, when the noble metal element is not a noble metal element deposited from the titanium alloy base material, for example, and the noble metal element is coated on the surface of the titanium alloy base material separately to form a mixed layer with titanium oxide, such excellent conductivity cannot be obtained. Moreover, since it becomes a pattern which coats separately like the said prior art, even if the original conductivity was ensured, when using it as a fuel cell separator etc., the problem of the adhesiveness and peeling of the film which the said prior art necessarily inevitably has Therefore, the conductivity is significantly degraded.

Moreover, even if the surface layer (film) provided on the surface of the titanium material for electrodes is made into the mixed layer of the noble metal element and titanium oxide derived from a titanium alloy base material like this invention, the manufacturing conditions of these mixed layers are bad or it is not optimal. Of course it can happen. In such a case, it is also important that the surface of the mixed layer and the titanium alloy base material have excellent conductivity such that the contact resistance value of the measurement method is 12 mΩ · cm ² or less, and the stability for a long time cannot be maintained.

In addition, as described later, the mixed layer of the precious metal element derived from the titanium alloy base material and the titanium oxide (whether or not it satisfies the required characteristics as a fuel cell separator, etc.) has the porosity and the film thickness of the titanium oxide constituting the mixed layer. Quantification and discrimination in terms of continuity and the like are very difficult because the mixed layer is very thin. Moreover, since good or bad of a mixed layer is not determined by a composition component or a systematic difference, it is also very difficult to quantify and discriminate metallurgically.

For this reason, the contact resistance value by the said measuring method in this invention is not a mere specification of a characteristic, but can replace determination by the said structure with respect to a mixed layer, or metallurgical quantification, determination, or correspond to this determination. It can also be said to be an important criterion or evaluation criterion of the mixed layer.

According to this invention, the titanium material for electrodes with a low contact resistance value and the electroconductivity stable for a long time can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing substitute photograph which shows the invention example mixed layer of the noble metal element and titanium oxide formed in the surface of the titanium material for electrodes.

Fig. 2 is a drawing substitute photograph showing a comparative example mixed layer of a noble metal element and titanium oxide formed on the surface of a titanium material for electrodes.

Fig. 3 is a drawing substitute photograph showing a comparative example mixed layer of a noble metal element and titanium oxide formed on the surface of a titanium material for electrodes.

4 is an explanatory diagram showing an apparatus for measuring contact resistance values.

To practice the invention  Best form for

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

(Titanium alloy base material)

The titanium alloy base material of this invention can be manufactured in desired shape, such as a board | plate and a wire rod, by the rolling, forging process, etc. by a conventional method. In order to deposit a noble metal element derived from the titanium alloy base material on the surface and to form a mixed layer of the precipitated noble metal element and the titanium oxide, as a premise, platinum group elements (Pd, Pt, Ir, Ru, Rh and Os) One or two or more alloying elements of the noble metal element selected from Au, Gold and Ag are contained.

As a titanium alloy base material as a base material which contains these noble metal elements, general-purpose pure titanium and general-purpose titanium alloy which satisfy | fill the mechanical characteristic calculated | required as a fuel cell separator etc. can be selected suitably. For example, application of the following titanium alloy (indicated alloy element amount in mass%) is illustrated.

Ti-0.4Ni-0.015Pd-0.025Ru-0.14Cr (14 kinds of JIS standard, 15 kinds), Ti-0.05Pd (17 kinds of JIS standard, 18 kinds), Ti-0.05Pd-0.3Co (19 kinds of JIS standard, 20 kinds), Ti-0.05Ru-0.5Ni (21 kinds, 22 kinds, 23 kinds of JIS standard), Ti-0.1Ru.

Moreover, in order to adjust mechanical properties, such as tensile strength, it is possible to add elements, such as 0, H, N, Fe, C, to a titanium alloy of a base material as needed. The surface state of the titanium alloy of the base material is not particularly limited, and ordinary pickling materials, bright annealing, polishing materials and the like are applicable.

(Content of precious metal element)

The precious metal element in the titanium alloy base material precipitates and concentrates on the surface of the base material to form a conductive layer as a result of Ti being selectively corroded and eluted in the precipitation treatment by an acid solution described later. Even if the content of the noble metal element is extremely small, increasing the amount of Ti eluted in the precipitation treatment ensures the amount of the deposited noble metal element, thereby forming a conductive layer effective for reducing the contact resistance.

However, when the content of the noble metal element previously contained in the titanium alloy base material is too small, the cost of Ti to elute becomes high, and a long time is required for the precipitation of the noble metal element. Moreover, when mixed layer formation conditions are bad including precipitation of a noble metal element, precipitation to the said titanium alloy base material may not be able to form a mixed layer with a titanium oxide. The possibility is not even if there is possible to form a mixed layer, the mixed layer can have excellent conductivity and stability over the long term to be in contact resistance due to the way the measured mixed-layer surface and the titanium alloy substrate with 12mΩ · cm ² or less There is this.

On the other hand, when there is too much content of a noble metal element, it becomes expensive and it cannot manufacture economical titanium material for electrodes. Moreover, there exists a possibility that the mechanical property and workability of the titanium material for electrodes may also be reduced. In addition, in order to form a mixed layer, as mentioned above, it is not necessary to contain a noble metal element in large quantities.

From these points, it is preferable that content of these noble metal elements in a titanium alloy base material is 0.005-1.0 mass% in the sum total of the noble metal element to contain. More preferably, it is 0.01-0.5 mass%, More preferably, you may be 0.03-0.3 mass%.

(Mixed layer of precious metal element and titanium oxide)

Next, the mixed layer of the noble metal element (crystal, particle | grain) and titanium oxide formed in the surface of the titanium material for electrodes in this invention is demonstrated below.

(pellicle)

The mixed layer of the noble metal element (crystal, particle) and titanium oxide in this invention is a thin film with an average thickness of 200 nm or less derived from a titanium alloy base material. In this respect, the coating or coating such that the above-described prior art separately coats the dissimilar material on the surface of the titanium material is a thick film in mm or μm, and in view of the thickness of the film, the precious metal element (crystal, particle) ) And a mixed layer of titanium oxide are characterized.

(Contact resistance value)

In the present invention, the characteristics of the mixed layer of the noble metal element and the titanium oxide are 12 mΩ · cm ² or less, preferably (more strictly) 9 mΩ · in the contact resistance value of the mixed layer surface and the titanium alloy substrate by the following measuring method. It has electroconductivity to be cm ² or less. A carbon material, which has been developed as a separator material in the past, is measured to have a contact resistance of about 15 mΩ · cm ² by the following measuring method. For this reason, the contact resistance value of the separator material of this invention was set to 12 m (ohm) * cm <^2> or less which was superior to this. When the said contact resistance value is too high, the current loss in use as an electrode titanium material or a separator will become large, and it is unsuitable as an electrode titanium material or a separator.

The contact resistance value characteristics are obtained by incorporating a mixed layer in a titanium alloy substrate in advance and by using a mixed layer of a noble metal element precipitated from the titanium alloy substrate and a titanium oxide produced by heat treatment of the titanium alloy substrate on which the precious metal element is deposited. Obtained. Since the mixed layer of the noble metal element and titanium oxide derived from a titanium alloy base material has the outstanding electroconductivity, and since corrosion resistance and durability are good, this electroconductivity is stable over a long period of time.

1 to 3 show a mixed layer of a noble metal element and a titanium oxide formed on the surface of a titanium material for electrodes as a cross-sectional structure photograph by TEM at 750000 magnification. 1 is a mixed layer of noble metal elements (crystals and particles) and titanium oxide formed on the surface of an electrode titanium material according to the present invention. This invention example of FIG. 1 is invention example 4 in the Example mentioned later, and produced the mixed layer on the preferable conditions (forming method) mentioned later.

On the other hand, FIG. 2 is a mixed layer of noble metal elements (crystals, particles) and titanium oxide, which differ only in the point of not being heat-treated, although the noble metal elements were precipitated under the preferable conditions described later as a comparison. This is a comparative example 2 in the Example mentioned later.

FIG. 3 is a mixed layer of noble metal elements (crystals, particles) and titanium oxide, which differ only in the point of heat treatment in an oxygen-rich air atmosphere, although a precipitate is precipitated under the preferable conditions described later. 3 is a comparative example 3 in Examples described later.

It can be seen from FIGS. 1 to 3 that the mixed layer is formed by mixing the precipitated noble metal elements (crystals and particles) and the titanium oxide particles.

In addition, the dense structure of the mixed layer as shown in FIG. 1 has a function of preventing titanium oxide particles from becoming a diffusion barrier of corrosive substances in the environment, thereby preventing a titanium alloy as a substrate. Therefore, it becomes a mixed layer which has corrosion resistance and durability, and stabilizes electroconductivity (conductive property) over a long period of time.

In contrast, the mixed layer of FIG. 2 has a large spacing and a sparse shape. Moreover, the film of titanium oxide in the titanium base material side in a mixed layer is thick and continuous. Moreover, although the mixed layer of FIG. 3 is dense, the film of titanium oxide in the titanium base material side in a mixed layer is thicker and continuous.

The mixed layer has, in the contact resistance value by the above measurement method, also the present invention is a mixed layer Comparative Example the mixed layer of 6mΩ · and cm ^2, this Comparative Example the mixed layer of Figure ² 37mΩ · cm 2, 3 of 1 402mΩ · cm ² There is a clear difference in contact resistance. As shown in the mixed layers shown in Figs. 2 and 3, when the voids are many and sparse, or when the titanium oxide film on the titanium substrate side in the mixed layer is thick and continuous, the contact resistance value necessarily becomes 12 mΩ · cm ² or less. Do not.

In addition, as shown in the mixed layer of FIG. 2, when the gap is large and sparse, corrosive substances such as chloride ions and sulfide ions penetrate into the environment to corrode the titanium alloy of the substrate. When the titanium alloy of the base material corrodes, peeling of the thickened layer occurs due to volume expansion caused by the corrosion product, or due to the electrical resistance of the corrosion product itself, the contact resistance rises and the conductivity decreases.

In contrast between the inventive mixed layer of FIG. 1 and the comparative example mixed layer of FIGS. 2 and 3, are there many voids (gaps) or dense, or is the film of titanium oxide on the titanium substrate side of the mixed layer thick, continuous, thin or discontinuous? The qualitative difference of, etc. can be seen. However, as described above, it is very difficult to quantify the difference between these mixed layers in terms of porosity, film thickness, continuity, etc. of the titanium oxide, because the mixed layer is very thin. In addition, these mixed layers are almost identical in composition and structure, and are difficult to discriminate metallurgically.

For this reason, the contact resistance value by the said measuring method in this invention is not a regulation of a simple characteristic as mentioned above. That is, the contact resistance value in the present invention can be used as a fuel cell separator or the like of the mixed layer, which can replace the mixed layer, the metallurgical quantification, or the determination by the above-described configuration, or can correspond to such discrimination. It is an important criterion or evaluation criterion of whether or not the required characteristic is satisfied.

(Measuring method of contact resistance value)

4 shows an embodiment of a device for measuring the contact resistance. In Fig. 4, 1 is a plate-like titanium alloy material, 2 is carbon cloth, and 3 is copper electrode. Here, both surfaces of the plate-shaped titanium alloy material 1 on which the mixed layer is formed are sandwiched between carbon cloths 2a and 2b each having an average thickness of 0.3 mm, and the titanium alloy material 1 from above the titanium alloy material 1. this with the contact area 1cm by ^two copper electrodes (3a), and the titanium alloy material 1 is from the lower side, the contact area with the titanium alloy material 1 1cm ² of copper electrode (3b) by, sandwiched between each . In addition, by the hydraulic press which is not shown in figure, surface pressure 5 kg / cm <^2> is loaded from both the upper and lower sides of the titanium alloy material 1 with the copper electrodes 3a and 3b and the carbon cloth 2a and 2b interposed therebetween. In this state, as shown in FIG. 4, when the current of 7.4 mA flows through the current line 4 between the two copper electrodes 3a and 3b, the two carbon cloths 2a and 2b are separated. It is assumed that a contact resistance is calculated using a four-terminal ohmmeter for measuring the voltage drop by the voltage line 5.

Since the four-terminal ohmmeter separates the current line 4 and the voltage line 5, the resistance of the wiring does not occur as an error, so that a relatively precise contact resistance can be measured.

The contact resistance value by this measuring method selects the stringent conditions which assumed the use of the said carbon cloth and the use of the said surface pressure actual separator also as a measuring method. In addition, the strict conditions are similarly selected as the contact resistance value.

If these measurement conditions differ, naturally the contact resistance obtained will also change. The contact resistance value hardly changes in the range of the normal titanium alloy plate for electrodes whose plate | board thickness of the titanium alloy material 1 is 0.3-3.0 mm. However, if, for example, the surface pressure by the hydraulic press is higher, the contact resistance value decreases, which is not suitable for the evaluation in the case where the use in the actual separator is assumed, and may be unsuitable for the actual separator. have. The same applies to the case where the gold plating is applied to the contact surface of the measuring electrode, and the carbon cloth is not used.

(Thickness of mixed layer)

As mentioned above, the mixed layer of the noble metal element (crystal, particle) and titanium oxide in this invention is a thin film whose average thickness derived from a titanium alloy base material is 200 nm or less. If a mixed layer is to be formed from a noble metal element (crystal, particle) and titanium oxide derived from a titanium alloy base material, it is difficult to thicken the average thickness beyond 200 nm, and there is no need for it. Therefore, the average thickness of the mixed layer defined in the present invention is 200 nm or less, in order to distinguish it from a coating or coating such as a separate coating of a different material, which is a thick film in mm or μm, on the surface of a titanium material, as described above. .

However, there is also a preferred thickness in the mixed layer of the noble metal element (crystal, particle) and titanium oxide in the present invention, and the average thickness of the mixed layer is preferably 10 to 100 nm. If the average thickness is too thin, the corrosion resistance and durability deteriorate in the short term. On the other hand, when the average thickness is too thick, the oxide layer becomes thick, so that Pd cannot conduct the outermost surface of the mixed layer and the base material, and there is a possibility that the contact resistance value does not become 12 mΩ · cm ² or less. Moreover, a film stress becomes large, peeling and a crack occur easily in a mixed layer, and corrosion resistance and durability also fall.

As shown in Fig. 1, the average thickness of the mixed layer is a TEM (transmission electron microscope) with a magnification of 75000, and observes, measures and averages 10 surface areas at arbitrary portions of the titanium material central portion.

(Noble metal element content of mixed layer)

It is preferable that the average content of the noble metal element in the mixed layer of a noble metal element and a titanium oxide is 1-90 atomic% in total. If the content of the noble metal element in the mixed layer is too small, there is a possibility that the contact resistance value of the mixed layer does not become ¹² mΩ · cm ² or less. On the other hand, in order to make the contact resistance value of a mixed layer into 12 m (ohm) * cm <^2> or less, it is not necessary to contain much noble metal element.

The noble metal element content of this mixed layer measures and averages 10 arbitrary surface layer parts (concentrated layers of a noble metal element) by the X-ray photoelectron spectroscopy (XPS), for example. Thereby, the density | concentration of Ti and a noble metal element is measured along a depth direction, and a concentration profile is obtained. In this concentration profile, the concentrations of the noble metal element and Ti at the depth at which the noble metal element concentration shows the peak are read, and their ratio, that is, 100 x B1 / (A + B1), is defined as the concentration of the noble metal element in the concentrated layer. . In addition, when the noble metal element concentration does not show a peak, the ratio of the concentration of the noble metal element and Ti at the outermost surface is taken as the noble metal element concentration.

Here, the concentration of the noble metal element in the concentrated layer of the noble metal element is a ratio of the amount of the noble metal element (total amount) to the total amount of Ti in the concentrated layer of the noble metal element and the amount of the noble metal element (total amount). That is, when Ti amount in the concentrated layer of the noble metal element is A and the amount of the noble metal element (total amount) is B, the concentration (atomic%) of the precious metal element in the concentrated layer of the noble metal element is 100 × B / (A + B). . In the case where two kinds of precious metal elements are included, each amount of B ₁ and B ₂ is B = B ₁ + B ₂ , and the concentration (atomic%) of the precious metal element in the concentrated layer of the precious metal element is 100 × ( B ₁ + B ₂ ) / (A + B ₁ + B ₂ ). In the case where three kinds of precious metal elements are included, the amount of B ₁ , B ₂ and B ₃ is B = B ₁ + B ₂ + B ₃ , and the concentration of the precious metal element in the concentrated layer of the precious metal element (atoms %) = 100 × (B ₁ + B ₂ + B ₃ ) / (A + B ₁ + B ₂ + B ₃ ).

(Production method of mixed layer)

Preparation of the mixed layer of a noble metal element and a titanium oxide in this invention is first performed by precipitating a noble metal element from a titanium alloy base material on a surface of a base material, and then generating a titanium oxide newly on the surface of the titanium alloy base material which precipitated a noble metal element.

According to the method for preparing such a mixed layer, the initial contact resistance is low, the corrosion resistance is excellent, the durability is high, the contact resistance hardly rises over a long period of time, and the drop in conductivity is unlikely to occur. It is hard to produce the fall of electroconductivity by this, and the titanium material for electrodes which can maintain high electrical conductivity can be obtained.

(Acid solution treatment)

Precipitation of the noble metal element from the titanium alloy substrate to the substrate surface is performed by an acid solution treatment containing a non-oxidizing acid and an oxidizing acid of the titanium alloy substrate.

When a titanium alloy base material is immersed in the acid solution containing non-oxidizing acid, a trace amount of a noble metal element dissolves in a solution. When the solution contains a non-oxidizing acid and an oxidizing acid, the precious metal element dissolved in the trace amount is reprecipitated in the solution to promote the concentration of the precious metal element on the surface of the titanium alloy base material. It becomes easy to form the precipitation layer (concentration layer) with high density | concentration sufficiently.

In addition, an oxidizing acid is an acid which has the characteristics like forming an oxide film on the surface of these metals when a titanium alloy base material is immersed in this acid solution. A non-oxidizing acid is an acid which does not have the characteristic of forming an oxide film on the surface of these metals when a titanium alloy base material is immersed in this acid solution.

The solution containing the non-oxidizing acid may be mixed by adding a non-oxidizing acid to a solvent such as water, or may be dissolved in a solvent such as water to form a salt (eg, ferric chloride) which becomes a non-oxidizing acid. It may be added to such a solvent and dissolved. These can all be used as a solution containing a non-oxidizing acid. The solution containing the oxidizing acid may be a mixture of an oxidizing acid added to a solvent such as water, or may be dissolved in a solvent such as water. . These can all be used as a solution containing an oxidizing acid. The solution is not limited to an aqueous solution, and may be a non-aqueous solution in which an acid is dissolved in an organic solvent or the like.

As an oxidizing acid, nitric acid is preferable. When it contains 0.1-40 mass% of nitric acid, reprecipitation of the said noble metal element arises more reliably, and can accelerate surface precipitation (concentration) of a noble metal element more. When the concentration of the nitric acid is less than 0.1% by mass, the effect of promoting the surface thickening is lowered. When the concentration of the nitric acid is more than 40% by mass, the passivation of Ti occurs, making it difficult to selectively dissolve Ti. It tends to be difficult to form a precipitation (thickening) layer. For this reason, the concentration of nitric acid is preferably 0.1 to 40% by mass, more preferably 1 to 30%. In consideration of the adhesion of the noble metal element precipitation (concentration) layer, the concentration of nitric acid is more preferably 1 to 20% by mass.

As the non-oxidizing acid, hydrogen fluoride (HF), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₃ ), formic acid (HCOOH), and oxalic acid [(COOH) ₂ ] are preferable.

When these acids contain the following predetermined amounts, it is possible to more reliably form a precipitation (concentration) layer having a sufficiently high concentration of the precious metal element. When the concentration of these acids is low, for example, when the concentration of hydrochloric acid is less than 1.0% by mass, the rate of selective dissolution of Ti becomes very slow. For this reason, it becomes difficult to form the precipitation (concentration) layer with high concentration of a noble metal element in the range of practical processing time.

On the other hand, when the concentration of these acids is high, the selective dissolution rate of Ti is very fast. For this reason, even if a concentrated layer of a precious metal element is produced once, it falls off in an instant, and as a result, an effective precipitation (concentration) layer is hardly obtained, and even if a precious metal element precipitation (concentration) layer is obtained, the adhesion tends to be not so good. .

For this reason, the concentration of the non-oxidizing acid is, for example, hydrogen fluoride (HF): 0.01 to 3.0 mass%, preferably 0.05 to 2.0 mass%, hydrochloric acid (HCl): 1.0 to 30 mass%, preferably 2.0 to 25 mass%, sulfuric acid (H ₂ SO ₄ ): 1.0 to 30 mass%, preferably 2.0 to 25 mass%, phosphoric acid (H ₃ PO ₃ ): 10 to 50 mass%, preferably 15 to 45 mass%, Formic acid (HCOOH): 10 to 40% by mass, preferably 15 to 35% by mass, oxalic acid [(COOH) ₂ ]: 10 to 30% by mass, preferably 15 to 25% by mass.

In addition, these acids can be used in combination of 2 or more type. When using two or more types in combination, each concentration may be set to a concentration at which the selective dissolution rate of Ti is too fast and the precipitation (concentration) layer of the noble metal element produced once is eliminated.

When the titanium alloy is immersed in an acid solution containing a non-oxidizing acid and an oxidizing acid, if the treatment temperature (solution temperature) is too low, the reaction rate is slow. For this reason, it takes a long time to form the precipitation (concentration) layer of the noble metal element, and if the treatment temperature is too high, the dissolution reaction becomes uneven, and the site where the precipitation (concentration) of the noble metal element is insufficient is likely to occur. From this point of view, the treatment temperature is preferably set to 10 to 80 캜, more preferably 15 to 60 캜.

If the treatment time is too short, it becomes difficult to form a sufficient (precipitated) layer of sufficient noble metal elements. The durability and stability also decreases. If the treatment time is somewhat longer, a stable surface layer on which noble metal elements precipitate (concentrate) is formed. Since the reaction becomes difficult to proceed, the effect is saturated. Although slightly different depending on the composition of the solution immersed in the titanium alloy and the treatment temperature, it is recommended that the treatment time be approximately 1 to 60 minutes.

(Heat treatment)

As described above, the production of the titanium oxide based on the titanium alloy after precipitation of the noble metal element is preferably performed by heat treatment in a low oxygen concentration atmosphere with an oxygen partial pressure of 10 ⁻² Torr (1.33 Pa) or less and a temperature of 350 to 800 ° C. Do. When the low oxygen concentration atmosphere, the type of atmosphere is not correlated, as described below, since the influence of the oxygen concentration in size, is preferably performed in a vacuum atmosphere, an inert gas (Ar, N _2, etc.) or a reducing atmosphere.

When the titanium alloy substrate after the precious metal element is precipitated is heated in the low oxygen concentration atmosphere, as shown in Fig. 1, the contact resistance value is small and dense and the film of titanium oxide on the titanium substrate side is discontinuous. This mixed layer of 12 m ohm cm ² or less can be produced.

This is, when heated in a low oxygen concentration atmosphere, the reaction of oxygen on the oxide surface and titanium of the base material speeds up the reaction (inner diffusion of oxygen in the titanium oxide is suppressed). For this reason, titanium diffuses outward (surface), fine titanium oxide particles are formed between the noble metal elements (crystals and particles) in which the precipitated (condensed) particles are densified, and a film of titanium oxide on the titanium substrate side is developed. It is presumed to be due to being difficult to do.

On the other hand, when the oxygen partial pressure of the atmosphere exceeds 10 ^-2 Torr (1.33 Pa) and the oxygen concentration increases or the temperature rises above 800 ° C, the inner diffusion of oxygen in the titanium oxide (to the base metal side) Diffusion into the rate. For this reason, the growth of the oxide of titanium becomes remarkable, and the film of the titanium oxide on the titanium base side is thick and continuous, and it becomes exactly the mixed layer like FIG. 3 mentioned above, and increases a film contact resistance.

When the temperature of this heating is less than 350 degreeC, it becomes the same as the case of not heat-processing, and becomes a sparse mixed layer with many voids like FIG.

An embodiment of the present invention will be described below. In addition, this invention is not limited to this Example, It is also possible to change suitably and to implement in the range which may be suitable for the meaning of this invention, and all of them are contained in the technical scope of this invention.

( Example  One)

The mixed layer of a noble metal element and a titanium oxide was formed on the surface of the various titanium alloy plates containing the noble metal element shown in Table 1, the contact resistance of this titanium alloy plate was measured, and the performance as an electrode titanium material was evaluated.

Specifically, various titanium alloy plates containing noble metal elements having a width of 30 mm, a length of 30 mm, and a plate thickness of 1.0 mm were dry polished to SiC # 400 as a pretreatment, followed by ultrasonic cleaning in acetone. Then, it was immersed in the acid aqueous solution containing 10 mass% nitric acid concentration as a non-oxidizing acid, and 0.25 mass% hydrogen fluoride as a non-oxidizing acid, respectively. The temperature of aqueous solution was 25 degreeC, and immersion time was 10 minutes. Next, the titanium alloy plate in which the precious metal element was deposited on the surface by immersion treatment in these acid aqueous solutions was subjected to vacuum heat treatment at 500 ° C. × 30 minutes under an oxygen partial pressure of 10 ⁻⁵ Torr (1.33 × 10 ⁻³ Pa). The mixed layer of the produced titanium oxide and the said noble metal element was formed in the surface of a titanium alloy plate, and it was set as the test material.

As a comparative example, the test material of the example which did not heat-treat the titanium alloy plate after the immersion process in the said acid aqueous solution on the same conditions, and the example which heat-processed 500 degreeC * 30 minutes in air | atmosphere was also prepared.

The measurement of the contact resistance of these test materials was performed by the method mentioned above using "MODEL3566" by Tsurugadenki Corporation as a four-terminal ohmmeter. As the durability evaluation of this mixed layer, the use as a fuel cell separator was simulated, and after the corrosion test of immersion in an aqueous sulfuric acid solution at 80 ° C. and pH 2 for 3000 hours, the contact resistance was measured again by the above method, and the two were compared. The durability was evaluated.

The structure of the noble metal element (crystal, particle) and the titanium oxide mixed layer was analyzed by the transmission electron microscope (TEM) to evaluate which mixed layer structure of Figs.

The thickness of the noble metal element and the titanium oxide mixed layer and the noble metal element content of the mixed layer were also measured by the above-described analysis method. These results are shown in Table 1.

As shown in Table 1, each invention example including invention example 4 precipitates a noble metal element from the titanium alloy plate on the surface by the immersion treatment in the said preferable acid aqueous solution, and performs the said preferable vacuum heat processing, The mixed layer of the said noble metal element and titanium oxide similar to the invention example 4 shown in the said FIG. 1 is formed in the surface of a titanium alloy plate.

As a result, each invention example has electroconductivity that the surface of this mixed layer and a titanium alloy base material become 9 m (ohm) * cm <^2> or less in the contact resistance value by the said measuring method. Moreover, even after a corrosion test, it has electroconductivity to become 9 m (ohm) * cm <^2> or less from the contact resistance value by the said measuring method.

Therefore, each invention example has a low contact resistance, and since the low value is maintained even after a corrosion test, it can be said that it is a material which has the extremely outstanding contact resistance characteristic.

On the other hand, in each comparative example in which only an acid solution immersion was performed and no heat treatment was performed, a mixed layer of the noble metal element and titanium oxide, similar to Comparative Example 2 shown in FIG. 2, was formed on the surface of the titanium alloy plate.

Moreover, although the acid solution immersion was carried out, each comparative example in which the heat treatment was performed in an atmospheric atmosphere having a high oxygen concentration instead of the vacuum heat treatment is the same as the comparative example 3 shown in FIG. 3, and the noble metal element and titanium oxide. Of a mixed layer is formed on the surface of the titanium alloy plate.

As a result, in each said comparative example, the contact resistance value of this mixed layer surface and a titanium alloy base material exceeds 12 m (ohm) * cm < ² >. Moreover, all the contact resistance values became higher even after the corrosion test.

Therefore, each of the above comparative examples has a high contact resistance and also a high contact resistance after the corrosion test, which is remarkably inferior in contact resistance characteristics. This is also the same as Comparative Example 1 in which no acid solution immersion or heat treatment is performed and the mixed layer is not formed on the titanium alloy plate surface.

( Example  2)

After depositing Pd on the surface of the Ti-0.15Pd titanium alloy plate, as shown in Table 2 below, the temperature of the vacuum heat treatment was changed in various ways, and the mixed layer of Pd and titanium oxide, which are noble metal elements on the surface of the titanium alloy plate, were changed. Was formed, the contact resistance of this titanium alloy plate was measured, and the durability as a titanium material for electrodes was evaluated.

Specifically, the same pretreatment as in Example 1 was performed on the Ti-0.15Pd titanium alloy plate processed to the same size as in Example 1. However, the immersion time of the acid aqueous solution containing nitric acid and hydrogen fluoride was 30 minutes. Next, by the immersion treatment in these acid aqueous solutions, vacuum heating treatment was performed on the titanium alloy plate in which Pd was deposited on the surface, and a mixed layer of the produced titanium oxide and Pd was formed on the surface of the titanium alloy plate to prepare a specimen. At this time, the vacuum heat treatment changed the heating temperature to 200 to 850 ° C. in a furnace in which the oxygen partial pressure was set to 10 ⁻⁵ Torr (1.33 × 10 ⁻³ Pa) in common. In addition, heating time was made into 30 minutes in common.

The contact resistance of these test materials was measured in the same manner as in Example 1. In addition, the durability evaluation of this mixed layer was also carried out in the same manner as in Example 1, and after the corrosion test simulating the use as a fuel cell separator, the contact resistance measurement was again performed by the above-described method, and both were compared to evaluate the durability.

The structure, thickness, and Pd element content of the Pd (crystals and particles) and the titanium oxide mixed layer were also subjected to structural analysis and analysis in the same manner as in Example 1 above. These results are shown in Table 2.

As shown in Table 2, each invention example of invention examples 28-33 precipitates Pd from the titanium alloy plate in the surface by the immersion process in the said preferable acid aqueous solution, and is preferable 350-800 degreeC heating temperature. Vacuum heat treatment was performed in the range. For this reason, the mixed layer of Pd and titanium oxide of the same kind as invention example 4 (Table 1) shown in the said FIG. 1 is formed in the surface of a titanium alloy plate.

As a result, the invention examples 28-33 have the electroconductivity that this mixed layer surface and a titanium alloy base material will be 12 m (ohm) * cm <^2> or less in the contact resistance value by the said measuring method, respectively. Moreover, even after a corrosion test, even the contact resistance value by the said measuring method has electroconductivity which becomes 12 m (ohm) * cm <^2> or less, respectively. Therefore, Examples 28 to 33 have a low contact resistance, and since the low value is maintained even after the corrosion test, it can be said to be a material having extremely excellent contact resistance characteristics.

On the other hand, Comparative Examples 26 and 27 in Table 2 have too low a temperature in vacuum heating treatment, so that the densification of the mixed layer and diffusion of oxygen into the mixed layer are insufficient, so that Comparative Example 2 (Table 1) shown in FIG. The mixed layer of the said noble metal element and titanium oxide of the same kind is formed in the surface of a titanium alloy plate. On the other hand, in Comparative Example 34, the temperature in the vacuum heat treatment is too high. For this reason, growth of the oxide of titanium is accelerated | stimulated, and the mixed layer of the said noble metal element and titanium oxide of the same kind as the comparative example 3 (Table 1) shown in said FIG. 3 is formed on the surface of a titanium alloy plate.

As a result, in each said comparative example, either the contact resistance value of this mixed layer surface and a titanium alloy base material, or the contact resistance value after a corrosion test exceeds 12 m (ohm) * cm < ² >. Therefore, each of the above comparative examples has a high contact resistance and also a high contact resistance after the corrosion test, which is remarkably inferior in contact resistance characteristics.

( Example  3)

After depositing Pd on the surface of the Ti-0.15Pd titanium alloy plate, the degree of vacuum in the furnace in the vacuum heating treatment is varied as shown in Table 3 to form a mixed layer of Pd and titanium oxide on the surface of the titanium alloy plate. The contact resistance of this titanium alloy sheet was measured, and the durability as a titanium material for electrodes was evaluated.

Specifically, the Ti-0.15Pd titanium alloy sheet having the same size as in Example 1 was pretreated in the same manner as in Example 2. Next, the vacuum heating process was performed about the titanium alloy plate which precipitated Pd on the surface by the immersion process in these acid aqueous solution.

In the vacuum heat treatment, once the inside of the heat treatment furnace is vacuumed at 10 ⁻⁴ Torr (1.33 × 10 ⁻² Pa) at an oxygen partial pressure, a small amount of nitrogen gas or argon gas is introduced into the furnace, and the degree of vacuum in the furnace is shown. As shown in Fig. 3, 0.1 Torr (1.33 × 10 ¹ Pa), 10 Torr (1.33 × 10 ³ Pa), and 760 Torr (1.01 × 10 ⁵ Pa) (atmospheric pressure) were respectively changed. Moreover, the comparative example made the inside of a furnace into the air atmosphere which does not introduce nitrogen gas or argon gas, and changed the vacuum degree in a furnace to 0.1 Torr (1.33 * 10 <^1> Pa) and 100 Torr (1.33 * 10 <^4> Pa), respectively. And in these furnace vacuum states, it heat-processed on 500 degreeC * 30 minute conditions in common, and the produced mixed layer of the titanium oxide and Pd was formed in the titanium alloy plate surface, and it was set as the test material.

The contact resistance of these test materials was measured in the same manner as in Example 1. In addition, the durability evaluation of this mixed layer was also carried out in the same manner as in Example 1, after the corrosion test simulating the use as a fuel cell separator, the contact resistance measurement was again performed by the above-described method, and both were compared to evaluate the durability. .

The structure, thickness, and Pd content of the Pd (crystals and particles) and the titanium oxide mixed layer were also subjected to structural analysis and analysis in the same manner as in Example 1 above. These results are shown in Table 3.

As shown in Table 3, each of the invention examples of the invention examples 35 to 40 introduces nitrogen gas or argon gas into the furnace, and since the furnace is maintained at a low oxygen partial pressure, invention examples 35 and 36 having a relatively low vacuum degree in the furnace. , 38, 39, as well as inventive examples 37 and 40 in which the vacuum degree in the furnace is almost at atmospheric pressure, a titanium alloy sheet containing a mixed layer of Pd and titanium oxide, similar to Inventive Example 4 (Table 1) shown in FIG. Formed on the surface.

As a result, the invention examples 35-40 have the electroconductivity which the surface of this mixed layer and a titanium alloy base material become 12 m (ohm) * cm <^2> or less in the contact resistance value by the said measuring method, respectively. Moreover, even after a corrosion test, even the contact resistance value by the said measuring method has electroconductivity which becomes 12 m (ohm) * cm <^2> or less, respectively. Therefore, inventive examples 35 to 40 are low in contact resistance and low in value even after the corrosion test, and thus can be said to be materials having extremely excellent contact resistance characteristics.

On the other hand, Comparative Examples 41 and 42 in Table 3 are lower than atmospheric pressure, but because the oxygen partial pressure in the furnace is high, Pd is similar to Comparative Example 3 (Table 1) shown in FIG. The mixed layer of and titanium oxide is formed on the surface of a titanium alloy plate.

As a result, in each of the above comparative examples, none of the contact resistance value between the surface of the mixed layer and the titanium alloy substrate and the contact resistance value after the corrosion test exceeded ¹² mΩ · cm ² . Therefore, each of the above comparative examples has a high contact resistance and also a high contact resistance after the corrosion test, which is remarkably inferior in contact resistance characteristics.

In addition, when nitrogen gas or argon gas is introduced into the furnace from the comparison of the results of the invention examples and comparative examples shown in Table 3, it has excellent contact resistance characteristics even if the vacuum degree in the furnace is low, but the vacuum degree in the furnace is higher (lower pressure ), It is understood that the contact resistance characteristics are more excellent.

The electrode titanium material obtained by the method for producing an electrode titanium material according to the present invention has a low initial contact resistance, excellent corrosion resistance, high durability, and difficult to increase contact resistance over a long period of time, so that deterioration of conductivity is unlikely to occur. . Therefore, it can be used suitably for the electrode which requires such a characteristic, it is especially suitable for the separator of a fuel cell, it is hard to raise a contact resistance for a long time, and can maintain high electrical conductivity.

Claims (25)

On the surface of the titanium alloy substrate containing one or two or more kinds of precious metal elements selected from platinum group elements, Au and Ag, a titanium material for separator of a fuel cell in which a mixed layer of precious metal elements and titanium oxides having an average thickness of 200 nm or less is formed. As a manufacturing method, The noble metal element is removed from the titanium alloy substrate by immersing the titanium alloy substrate containing one or two or more precious metal elements selected from platinum group-based elements, Au, and Ag in an acid solution containing a non-oxidizing acid and an oxidizing acid. Precipitating, and Heat-treating the titanium alloy substrate on which the precious metal element is deposited, thereby forming a mixed layer of the precious metal element and the titanium oxide Method for producing a titanium material for separator of the fuel cell, characterized in that it comprises a. The method of claim 1, The surface of the mixed layer and the titanium alloy substrate have a conductivity such that the contact resistance value is 12 mΩ · cm ² or less, The contact resistance was, the mixed layers are formed of plate-like titanium alloy material with a two-sided, a carbon cloth having an average thickness of 0.3mm between each of the titanium alloy, the contact area with the titanium alloy material 1cm from the upper electrode ² of copper and titanium alloys Insert the copper electrode having a contact area with the titanium alloy material of 1 cm ² from the lower side, respectively, and then, by hydraulic press, the copper electrode and the carbon cloth were sandwiched between each other, and a surface pressure of 5 kg / cm ² was obtained from the upper and lower sides of the titanium alloy material. A fuel, characterized in that the voltage drop between the two carbon cloths when a current of 7.4 mA flows between the two copper electrodes in a loaded state is measured by using a four-terminal ohmmeter. The manufacturing method of the titanium material for separators of a battery. The method of claim 1, The heat treatment is performed in a low oxygen concentration atmosphere having an oxygen partial pressure of 1.33 Pa (10 ⁻² Torr) or less and a temperature of 350 to 800 ° C., wherein the titanium material for separator of a fuel cell is used. The method of claim 2, The heat treatment is performed in a low oxygen concentration atmosphere having an oxygen partial pressure of 1.33 Pa (10 ⁻² Torr) or less and a temperature of 350 to 800 ° C., wherein the titanium material for separator of a fuel cell is used. The method of claim 1, The oxidizing acid is nitric acid, and the non-oxidizing acid is one or two or more of hydrogen fluoride, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and oxalic acid. The method of claim 2, The oxidizing acid is nitric acid, and the non-oxidizing acid is one or two or more of hydrogen fluoride, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and oxalic acid. The method of claim 3, wherein The oxidizing acid is nitric acid, and the non-oxidizing acid is one or two or more of hydrogen fluoride, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and oxalic acid. The method of claim 4, wherein The oxidizing acid is nitric acid, and the non-oxidizing acid is one or two or more of hydrogen fluoride, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid and oxalic acid. The method of claim 1, A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 2, The total content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to The manufacturing method of the titanium material for separators of a fuel cell which is 1.0 mass%. The method of claim 3, wherein A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 4, wherein A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 5, A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 6, A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 7, wherein A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 8, A method for producing a titanium material for separators in fuel cells, wherein the content of the precious metal element of the titanium alloy base material immersed in an acid solution is 0.005 to 1.0 mass% in total. The method of claim 1, The manufacturing method of the titanium material for separators of a fuel cell in the said mixed layer whose average content of the noble metal element when Ti and a noble metal element are made 100 atomic% in total is 1-90 atomic% in total. The method according to any one of claims 1 to 17, The manufacturing method of the titanium material for separators of a fuel cell whose average thickness of the said mixed layer is 10-100 nm. delete delete delete delete delete delete delete

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